Control of disalt in α-sulfofatty acid ester surfactants

ABSTRACT

In light colored surfactants produced by sulfonation of fatty acid alkyl esters with less than 2 moles of SO3 per mole of fatty acid alkyl ester and subsequent work-up of the crude sulfonate in aqueous medium to form salts, the content of  alpha -sulfofatty acid disalts is regulated and reduced by transesterifying the sulfonation product before its treatment with an aqueous medium with at least about 0.5 mole equivalent of an alcohol, based on the SO3 which is not for alpha -sulfonation.

This application is a division of application Ser. No. 753,304, filedJuly 10, 1985, now U.S. Pat. No. 4,695,409.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for regulating the disaltcontent in α-sulfofatty acid ester surfactants in the process for themanufacture thereof.

2. Description of Related Art

Wash-active substances based on α-sulfofatty acid esters or their saltshave been known for decades and numerous processes have been proposedfor their production (see e.g. U.S. Pat. No. 2,195,187, U.S. Pat. No.3,256,303 and U.S. Pat. No. 3,158,632). The salts of α-sulfofatty acidesters acting as wash-active substances are obtained by sulfonation oflower alkyl esters of saturated higher fatty acids with sulfur trioxide.In particular, fatty acid methyl esters which contain from 6 to 28carbon atoms in the fatty acid residue and which, apart from the CH₂-group in the α-position of the fatty acid residue, contain no othersulfonatable or sulfatable groups and which have an iodine number below5, are sulfonated with a sulfur trioxide-inert gas mixture and thereaction product is neutralized. Since dark-colored crude productsregularly accumulate during the sulfonation reaction, being unsuitablefor use in detergents and cleaners in that form, the crude sulfonationproduct has to be bleached. H₂ O₂ and/or hypochlorite in aqueoussolution is/are normally used for bleaching.

It is also known that considerable quantities of disalt of thecorresponding α-sulfofatty acids accumulate as an undesirable secondaryproduct during this sulfonation of fatty acid esters and during work-upof the α-sulfofatty acid ester crude product with aqueous media. Thesedisalts of the α-sulfofatty acids are undesirable for several reasons.First of all, they show only limited solubility in water. Secondly, theyexhibit poor surface activities Above all, however, they deteriouslyinfluence the viscosity of the aqueous ester sulfonate pastes ultimatelyproduced. An excessive content of the disalts accumulating as secondaryproduct leads to a considerable increase in the viscosity of the aqueousester sulfonate pastes which in turn gives rise to difficulties duringfurther processing of the ester sulfonate surfactant.

Considerable attention has been devoted, especially in recent years, tothis particular aspect of the production of surfactants based on estersulfonates. Numerous difficulties result, cf. U.S. Pat. No. 4,404,143and German Offenlegungsschrift No. 33 34 517. According to the first ofthese two publications a highly concentrated aqueous solution of a saltof α-sulfofatty acid esters is prepared by neutralizing the sulfonatedfatty acid ester product with an aqueous alkali solution in two stages,in the first of which the sulfonated product is neutralized to apH-value of from 2.5 to 4 with an aqueous alkali solution of relativelyhigh concentration (15 to 50% by weight of alkali) in the presence of aC₁ -C₄ alcohol in a quantity of from 5 to 20% by weight, based on theweight of the sulfonated product, after which neutralization iscompleted to a pH-value of from 6 to 7 in a second stage carried outwith a less concentrated aqueous alkali solution. The crude sulfonationproduct may optionally be bleached before this two-stage neutralization.To this end, an aqueous solution of H₂ O₂ is preferably used again inthe presence of a C₁ -C₄ alcohol. The hydrogen peroxide is supposed tobe used in the form of an aqueous solution having a concentration of 10%by weight or higher. The preferred alcohol is methanol where the fattyacid esters are methyl esters. Utilizing this technique is said toreduce the disalt content of the corresponding α-sulfofatty acids to 5%or lower.

However, the second of the two above-mentioned publications, GermanApplication No. 33 34 517, describes the disadvantages of this process.The sulfonation products obtained contain the short-chain alcohol usedin a large excess in the aqueous neutralized reaction product. Thesecomparatively large quantities of free alcohol are again undesirable fora number of reasons. They are troublesome, for example, during thework-up of surfactant mixtures of the above type in the production ofdetergent mixtures by spray-drying, particularly giving rise toundesirable pluming. In addition, the free alcohols present in thesurfactant mixture have an unpleasant odor which necessitatesdeodorization. To solve these problems, German Offenlegungsschrift No.33 34 517 proposes carrying out the aqueous bleaching and neutralizationof the crude α-sulfofatty acid esters in the presence of such quantitiesof a lower alcohol that an aqueous suspension containing from 30 to 55%by weight of the α-sulfofatty acid ester salt and, based on the weightof the α-sulfofatty acid ester salt, from 5 to 15% by weight of a loweralcohol sulfate and from 8 to 40% by weight of the lower alcohol isobtained. Finally, the aqueous suspension is said to be concentrated insuch a way that it contains from 40 to 65% by weight of α-sulfofattyacid ester salt, from 2 to 10% by weight of a lower alcohol sulfate andat most 2% by weight of a lower alcohol.

DESCRIPTION OF THE INVENTION

Other than in the operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients or reaction conditions usedherein are to be understood as modified in all instances by the term"about".

The present invention is based on the surprising observation that theundesirable formation of α-sulfofatty acid disalts can be prevented in avery much more practical manner. There is no need for large excesses ofalcohol to be used or for the optional subsequent step or concentrationby evaporation to eliminate unwanted alcohol. The process of the presentinvention is based on the realization that measured treatment of thecrude sulfonate of fatty acid alkyl esters with any alcohol in a small,but defined quantity, as explained hereinafter, results in thecontrollable reduction of the content of unwanted disalt. It is alsopossible by this measure to produce interesting ester mixtures ofα-sulfofatty acids which are distinguished, for example, by improvedflow properties during further processing.

Accordingly, the present invention relates to a process for regulatingand reducing the content of α-sulfofatty acid disalts in light-coloredsurfactants and surfactant mixtures which are produced by Sulfonation offatty acid alkyl esters with more than 1 and less than 2 moles of SO₃mole of fatty acid alkyl ester and subsequent work-up of the crudesulfonate in aqueous medium to form salts. In the process of theinvention, before the treatment with an aqueous medium, the sulfonationproduct is transesterified with at least about 0.5 mole equivalent of analcohol, based on the quantity of SO₃ which is not used forα-sulfonation.

In one particularly preferred embodiment of the process of theinvention, the free alcohol content of the reaction product is limitedat the same time. To this end, no more than about 2 mole equivalents ofthe free alcohol component are used in the transesterification stage.More particularly, no more than about 1 5 mole equivalents of thealcohol are used in the transesterification stage. These moleequivalents are again based on the quantity of SO₃ which is present inthe crude sulfonation product i e. which has not been used forα-sulfonation This S₃ reference base is calculated as the sum of twopartial amounts. One of these partial amounts corresponds to the SO₃excess which has been used in the sulfonation step (to increase theconversion) over and above the quantity of SO₃ required forα-sulfonation. The other partial amount is the difference between thequantity of SO₃ theoretically required and the amount actually used inthe α-sulfonation step.

The quantity of alcohol used for transesterification in each individualcase may be determined in part from the composition of the alcohol.Thus, in one preferred embodiment of the invention, alcohols which showcomparatively high reactivity in the transesterification step are usedin smaller quantities (within the ranges indicated) than less reactivealcohols. As a general rule, quantities of no more than about 1.3 moleequivalents of the alcohol, based on the excess quantity of SO₃described above, can be used with advantage; quantities of from 0.8 to1.3 mole equivalents of alcohol being preferred and quantities of from0.9 to 1.1 mole equivalents of alcohol being particularly preferred.

The conditions for the transesterification reaction are selected in sucha way, with particular allowance for the reactivity of the alcohol usedfor transesterification, that the additional heat load on the reactionmixture is kept to a minimum. In this way, the formation of undesirable,additional discolorations in the reaction product can be limited orprevented. However, the reaction conditions have to be sufficientlyintensive to bring about the transesterification required in accordancewith the invention. As a general rule, esterification is carried out attemperatures of from 40° to 150° C. and preferably at temperatures notexceeding 120° C. Suitable temperatures are temperatures above 60° C.and, more particularly, above 70° C. A suitable temperature range is,for example, 75° to 100° C. The reaction time is determined by, and isdependent on, the reactivity of the alcohol used fortransesterification, the reaction temperature selected, and the requiredreduction in the disalt content. In general, the reaction time is atleast 5 minutes and, more particularly, at least 10 minutes. Normally, areaction time of from 10 to 30 minutes is suitable.

The following general rule applies to the choice of the processconditions. Lower alcohols, particularly monohydric lower alcohols, forexample containing from 1 to 5 carbon atoms, show comparatively highreactivity in the transesterification reaction, although lowerpolyhydric alcohols also show comparatively high reactivity. In general,higher monohydric or polyhydric alcohols show lower reactivity Fattyalcohols or wax alcohols are examples of less reactive alcohols.Accordingly, their use requires more intensive reaction conditionswithin the above-stated limits.

As a consequence of the transesterification reaction, the free alcoholused for the reaction is bound in ester form to the α-sulfofatty acid.The alcohol component originally present in the fatty acid ester used issplit off as alcohol sulfate and, for example where fatty acid methylesters are used as starting material for the sulfonation reaction, ispresent as methyl sulfate in the reaction mixture aftertransesterification

The choice of the reaction components and reaction conditions within theparameters given above results in a disalt content in the reactionproduct treated with aqueous media and neutralized of less than 10% byweight, based on wash-active substance. Disalt contents of 5% or less byweight are preferred and can readily be obtained, although it ispossible to obtain even lower disalt contents, for example less than 2%by weight, using the process of the invention. Where highly reactivealcohols are used in the transesterification stage, hardly anydetectable alcohol is present in the ester sulfonate paste. Where lessreactive alcohols are used, limited quantities of the free alcohol usedin a small excess may be tolerated in the product to achieve acceptablereaction times in the reduction of the disalt content to below theindicated limits.

In principle, any alcohol can be used as the alcohol component for thetransesterification step. Accordingly , suitable alcohols are bothmonohydric alcohols and polyhydric alcohols. In one important embodimentof the invention, the same alcohol which is present in the fatty acidalkyl ester starting material is used for transesterification. Moreparticularly aliphatic C₁ -C₃ monoalcohols and the corresponding fattyacid alkyl esters are used with methanol and the corresponding fattyacid methyl esters are preferred. Since these lower alcohols andespecially methanol are distinguished by high reactivity in thetransesterification step, the quantity of free alcohol used can readilybe limited to the quantity which corresponds to the SO₃ that is not usedfor α-sulfonation. At the same time, comparatively milder conditions canbe applied with respect to temperature and/or reaction time. The resultof the transesterification step according to the invention is anα-sulfofatty acid alkyl ester, more particularly a methyl ester, inadmixture with a small quantity of methyl sulfate which is substantiallyfree from disalts and which does not contain any detectable quantitiesof free alcohol.

In one particularly important embodiment of the invention, however, thealcohols used for transesterification are different from those presentin the fatty acid ester starting material. In this case, too, thealcohols used may be divided into two basic groups, namely: monohydricand/or polyhydric alcohols which, on reaction with free SO₃, are capableof forming capillary-active surfactant-like sulfates, and monohydricand/or polyhydric alcohols which, on reaction with free SO₃, formnon-capillary-active sulfates.

The second of these two groups includes in particular alcoholscontaining a limited number of carbon atoms, for example monohydricalcohols containing no more than 9 carbon atoms. However, it alsoincludes lower polyols, for example ethylene glycol or glycerol. Thegroup of alcohols which, on reaction with free SO₃, are capable offorming capillary-active surfactant-like sulfates includes compoundswhich contain at least one hydrophobic residue and at least onealiphatically bound hydroxyl group on the molecule. The hydrophobicresidue present in these hydroxyl compounds can be a hydrocarbon residuecontaining at least 10 carbon atoms, more particularly an aliphatic orcycloaliphatic hydrocarbon residue. The hydrophobic residue can contain,for example, up to 30 carbon atoms.

This second group of alcohols includes, for example, saturated fattyalcohols or fatty alcohol mixtures of natural or synthetic origin orfatty acid alkylol amides. Like the starting material for thesulfonation step, these hydroxyl compounds can also have been obtainedfrom naturally occurring fats and oils. Instead of fatty alcohols orfatty acid alkylolamides such as these, it is possible to use any otherhydroxyl compounds which are capable of forming capillary-activesubstances upon reaction with free SO₃. Hydroxyl compounds such as theseinclude partial ethers of polyhydric alcohols with fatty alcohols andpartial esters of polyhydric alcohols with fatty acids, for examplepartial ethers and partial esters of ethylene glycol, propylene glycol,glycerol, pentaerythritol, mannitol, hexitol and also partial ethers andpartial esters of polyethylene and/or polypropylene glycols,polyglycerols, polypentaerythritol and the like. Suitable compounds are,above all, polyglycol ethers of the type obtained by the addition ofethylene and/or propylene oxide onto fatty alcohols, fatty acids, fattyacid amides or onto the partial ethers or partial esters of fattyalcohols and fatty acids containing dihydric, trihydric and polyhydricalcohols.

In one preferred embodiment, the alcohols used for transesterification ,apart from the hydroxyl group, contain no reactive groups in themolecule which are capable of undesirable secondary reactions.

Suitable alcohol components are, for example, monohydric aliphatic andcycloaliphatic C₁ -C₃₀ and preferably C₁ -C₂₄ such as methanol, ethanol,n-propanol, i-propanol, n-butanol, 2-butanol, n-pentanol, 2-pentanol,n-hexanol, n-octanol, n-decanol, n-dodecanol, n-tetradecanol,n-hexadecanol, n-octadecanol, n-eicosanol, n-docosanol, 2-hexyldecanol,2-octyldodecanol, 2-dodecylhexadecanol, C₉ -C₁₈ oxoalcohols, C₈ -C₂₀Ziegler alcohols, cyclohexanol and methylcyclohexanols; C₂ -C₃₀polyhydric aliphatic and cycloaliphatic alcohols, such as ethyleneglycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol,1,4-butylene glycol, hexamethylene glycol, polyethylene glycols,polypropylene glycols, glycerol, polyglycerols, trimethylol ethane,trimethylol propane, pentaerythritol, dipentaerythritol, mannitol,sorbitol, 1,2-cyclohexane diol and 1,3,5-cyclohexanetriol. The alcoholsmentioned may be used individually or in admixture in the process of theinvention. Commensurate with their origin, fatty alcohols in thenarrower sense, i.e. straight-chain aliphatic C₈ -C₂₄ alcohols, aregenerally used in the form of mixtures, the composition of thesemixtures being determined by the natural fats and oils which are used asstarting materials in their production.

Other examples of useful alcohol components are glycol semiethers, suchas methyl ethylene glycol, ethyl ethylene glycol and adducts of from 1to 20 moles of ethylene oxide and/or propylene oxide with aliphatic C₁-C₂₄ alcohols, particularly with fatty alcohols and fatty alcoholmixtures; glycol semi-esters, such as ethylene glycol monolaurate,ethylene glycol monomyristate and propylene glycol monostearate andadducts of from 1 to 20 moles of ethylene and/or propylene oxide withaliphatic C₁ -C₂₄ carboxylic acids, more especially with fatty acids andfatty acid mixtures; glycerol partial ethers and partial esters, such asglycerol monodecyl ether, glycerol monoacetate, glycerol diacetate,glycerol monopalmitate, glycerol distearate and ethylene oxide and/orpropylene oxide adducts of these glycerol derivatives; fatty acidalkanolamides, such as lauric acid monoethanolamide, lauric aciddiethanolaaide, stearic acid diethanolamide, and ethylene oxide and/orpropylene oxide adducts with carboxylic acid amides, particularly withfatty acid amides.

In the preferred embodiment of the process of the invention, the crudesulfonate to be subjected to transesterification should contain no morethan 50 mole % and preferably no more than 25 mole %, based on theα-sulfofatty acid ester formed of SO₃ which is not used in theα-sulfonation step. In addition, the degree of sulfonation of the fattyacid ester used as starting material in the crude sulfonates shouldpreferably be at least 90%, more preferably at least 95% and, betterstill, 98% or higher.

The sulfonation step preceding the transesterification step is carriedout in accordance with the teachings of the prior art, see for exampleU.S. Pat. No. 3,256,303 and U.S. Pat. No. 3,158,632. The startingmaterial for this sulfonation step is preferably a lower alkyl ester,more particularly the methyl ester, of fatty acids containing forexample from 6 to 28 and preferably from 8 to 18 carbon atoms. Thesefatty acid residues preferably emanate from natural fats of vegetables,land animals or aquatic animals. Apart from the hydrogen atom in theα-position, they should not contain any other sulfatable or sulfonatablegroups, particularly double bonds or alcoholic hydroxyl groups. Theiriodine numbers are below 5 and preferably below 2. Sulfonation iscarried out with an SO₃ -inert gas mixture which, normally, may containfrom 2 to 40% by volume of SO₃ at temperatures not exceeding or notsignificantly exceeding 100° C. and, preferably, not exceeding 95° C.The process can be carried out at a constant temperature or at atemperature adjusted in stages, as described in the above-mentionedpublications.

The transesterification step of the invention is followed by working upthe reaction product with aqueous media in known manner. This work-upstep comprises, in particular, the bleaching and neutralization of thecrude sulfonate transesterified in accordance with the invention.Bleaching can be carried out in known manner with aqueous hydrogenperoxide and/or hypochlorite solution. Neutralization can be carried outeither before or after bleaching. Acidic bleaching with hydrogenperoxide is described, for example, in U.S. Pat. No. 3,159,657, whileU.S. Pat. No. 3,452,064 describes a combined bleaching treatment inwhich an initially acidic peroxide bleaching operation is followed byneutralization of the sulfonated and partially bleached material, afterwhich bleaching is completed with hydrogen peroxide or, better still,with hypochlorite.

The process conditions used for bleaching and/or neutralization have tobe selected in such a way that the theoretically possible hydrolysis ofthe esters is precluded or suppressed as far as possible. In the absenceof these precautionary measures, the advantages of thetransesterification step of the invention with respect to reduction ofthe disalt content would be at least partly forfeited.

By reacting the crude sulfonic acid products with the alcohols inaccordance with the invention to produce the requiredtransesterification, it is possible not only to reduce the disaltcontent, but also to establish a broad spectrum of new ester sulfonatemixtures (for example methyl ester sulfonate+ester sulfonate of thealcohol used for transesterification) showing different performanceproperties. The invention thus opens up an interesting way of producingaqueous suspensions or pastes of ester sulfonates having a high contentof α-sulfofatty acid ester salts and, at the same time, a low viscosity.This low viscosity is achieved on the one hand through the reduction inthe undesired disalt content of the ester sulfonate paste, and on theother hand sulfonate ester mixtures can also lead to a reduction inviscosity in pastes of high fatty content (cf. German application No. 3334 517 cited above).

A general procedure for carrying out the transesterification reactionaccording to the invention is described in the following Examples whichare not given for purposes of limitation. The following Table shows theparticular alcohol components used for transesterification, the reactiontimes and reaction temperatures used, the molar ratio of the SO₃ notused for α-sulfonation in the crude sulfonate to the quantity of thealcohol used for transesterification and the values finally obtained forthe disalt content in % by weight, based on the wash-active substance.

EXAMPLES Examples 1 to 16

283 g (1 mole) of hardened tallow fatty acid methyl ester (iodine number0.5; saponfication number 198) were sulfonated with 96 g (1.2 moles) ofsulfur trioxide (5% by volume in air) at 90° C. in a falling-filmreactor. The resulting reaction mixture was then tempered for 30 minutesat 90° C. Thereafter the degree of sulfonation was 98%.

7.0 g (0.22 mole) of methanol were added to the tempered, crudesulfonation product with stirring at 90° C., followed by stirring for 20minutes at 90° C. 16 g of hydrogen peroxide in the form of a 35% byweight aqueous solution were added to the reaction product forbleaching, after which the product was stirred for 10 minutes at 60° C.before it was neutralized to pH 7 by the addition of a 25% by weightsodium hydroxide solution. In the solution of the neutral salt obtainedin this way, the disalt content amounted to 5.2% by weight, based on thetotal quantity of wash-active substance.

The disalt content was determined by potentiometric titration of anaqueous solution, adjusted to pH 2.5-3, of the bleached and neutralizedsulfonation product with sodium hydroxide solution, taking into accountthe fatty acid fractions present in the unsulfonated material.

In Examples 2 to 17, the procedure described above was modified to theextent that transesterification was carried out with the alcoholsindicated in the following Table instead of methanol. In Example 17, acomparison test was carried out under the same conditions as in Example1, but without transesterification between sulfonation and bleaching.

The results obtained in Examples 1 to b 16 are shown in the followingTable.

                  TABLE                                                           ______________________________________                                        Transesterification of crude sulfonation products of                          hardened tallow fatty acid methyl ester at 90° C.                                                   SO.sub.3 excess:                                                     Reaction alcohol Disalt                                   Example                                                                              Alcohol      time     (mole/mole                                                                            content                                  No.    component    (mins.)  equiv.) (% by wt)                                ______________________________________                                        1      methanol     20       1:1     5.2                                      2      ethanol      20       1:1     6.8                                      3      n-propanol   20       1:1     6.6                                      4      n-butanol    20       1:1     7.6                                      5      n-octanol    20       1:1     6.0                                      6      2-ethylhexanol                                                                             20       1:1     6.4                                      7      lauryl/myristyl-                                                                           20       1:1     5.5                                             alcohol (molar                                                                ratio 3:1)                                                             8      ethylene glycol                                                                            10       1:1     8.2                                      9      ethylene glycol                                                                            20       1:1     6.1                                      10     glycerol     10       1:1     9.1                                      11     glycerol     20       1:1     6.6                                      12     oleyl alcohol +                                                                            10       1:1     12.0                                            1 PO + 6 EO                                                            13     oleyl alcohol +                                                                            20       1:1     7.6                                             1 PO + 6 EO                                                            14     2-ethoxy ethanol                                                                           20       1:1     7.1                                      15     2-ethoxy ethanol                                                                           20         1:0.7 5.3                                      16     methanol     20       1:3     1.6                                      17     none (comparison                                                                           --       --      22.7                                            test)                                                                  ______________________________________                                    

What is claimed is:
 1. A process for the preparation of α-sulfofattyacid alkyl esters having a low disalt content comprising the steps of:A.sulfonating a fatty acid alkyl ester with more than 1 but less than 2moles of SO₃ per mole of fatty acid alkyl ester to produce anα-sulfofatty acid alkyl ester; B. At least partially transesterifyingthe α-sulfofatty acid alkyl ester from step A with an at least about 0.5mole equivalent, based on the quantity of SO₃ which is not used for aα-sulfonation of an alcohol different from the alcohol forming the estermoiety of the α-sulfofatty acid alkyl ester, at a temperature of fromabout 40° to about 150° C., to form a reaction mixture containingtransesterified α-sulfofatty acid alkyl ester and alkyl sulfate; and C.working up the product mixture from step B in an aqueous medium to formsalts of α-sulfofatty acid alkyl esters present in the mixture.
 2. Aprocess in accordance with claim 1, wherein from about 0.9 to about 1.1mole equivalents of the alcohol are used for transesterification in stepB.
 3. A process in accordance with claim 1, wherein the temperature instep B is from about 70 to about 120° C.
 4. A process in accordance withclaim 1, wherein the temperature in step B is from about 75 to about100° C.
 5. A process in accordance with claim 1 wherein the alcoholmoiety in the fatty acid alkyl ester starting material in step A isderived from one or more aliphatic C₁ -C₃ monoalcohols.
 6. A process inaccordance with claim 5 wherein the fatty acid alkyl ester startingmaterial is a methyl ester.
 7. A process in accordance with claim 1,wherein the alcohol in step B is a monohydric alcohol, a polyhydricalcohol, or a mixture of the foregoing which form capillary-activesurfactant-like sulfates upon reaction with free SO₃.
 8. A process inaccordance with claim 1, wherein the alcohol in step B is a monohydricalcohol, a polyhydric alcohol, or a mixture of the foregoing which formnoncapillary-active sulfates upon reaction with free SO₃.
 9. A processin accordance with claim 1 wherein in step A the resulting reactionmixture contains no more than 50 mole % free SO₃ based on a α-sulfofattyacid ester.
 10. A process in accordance with claim 9 wherein no morethan about 25 mole % of free SO₃ is present.
 11. A process in accordancewith claim 1 wherein the degree of sulfonation of the fatty acid alkylester starting material in step A is at least 90%.
 12. A process inaccordance with claim 11 wherein the degree of sulfonation is at least95%.
 13. The process of claim 1, wherein the alcohol in step B is a C₁-C₅ monohydric or polyhydric alcohol.
 14. The process of claim 1 whereinin step B the reaction mixture also contains non-transesterifiedα-sulfofatty acid alkyl ester.